Prepare the vegetables. Roughly chop the onion, carrots, celery, and green onions. Peel the garlic cloves and prepare the fresh herbs.
Sauté the vegetables. Set the Instant Pot to Sauté and add a little olive oil. Add the onion, carrots, celery, green onions, and garlic. Sauté for 3–5 minutes, stirring occasionally, until the vegetables begin to soften and become fragrant.
Add the herbs and water. Add the fresh thyme, rosemary sprigs, bay leaf, and water. Stir gently.
Pressure cook. Secure the lid and set the valve to Sealing. Cook on High Pressure for 15 minutes.
Release the pressure. Allow the pressure to release naturally for 10 minutes, then carefully release any remaining pressure.
Strain the broth. Carefully strain the broth through a fine-mesh strainer into a heat-safe bowl or container. BROTH WILL BE VERY HOT! Discard the cooked vegetables and herbs.
Season and use. Taste the broth and add salt if desired. Use it immediately in your favorite soups and stews, or let it cool before refrigerating or freezing.